Injection molding consists of heating and homogenizing plastic granules in a cylinder until they are sufficiently fluid to allow for pressure injection into a relatively cold mold where they solidify and take the shape of the mold cavity. The major advantages of the injection-molding process are the speed of production, minimal requirements for post molding operations and simultaneous multi-part molding. One disadvantage of the injection molding process is that the molds are generally expensive to manufacture.
In certain cases, it is desired that certain impressions in a multi-impression injection tool or mold should be "shut-off". This can arise if certain impressions are found to be defective or not capable of molding satisfactorily. More frequently, however, this requirement occurs when the tool comprises a set of dissimilar components and it is desired to make certain pieces and not others (e.g., components consisting of either right or left-hand pieces of an assembly, etc.). If the cut-off is to be semi-permanent, it is the practice to weld up the runner or runner gate. However, if the cut-off is temporary, merely to afford a selection in production or a change in quantity, the runner system can be designed to accommodate a plug that can be turned so that the runner may be allowed to continue or be shut-off. Sometimes two interchangeable plugs are employed, one being blank for shutting off the runner and the other being shaped to continue the runner. Commonly the mold (or mold halves) have to be removed from the molding machine and disassembled to change these plugs which is very costly and time consuming. (See "Injection-Mould Design Fundamentals", by Glanvill and Denton, Industrial Press Inc., 1965, N.Y., p.122).
What is needed is a means and method by which the flow to runners can be switched or cutoff in a simple and straight forward manner without having to disassemble mold halves and without having to use highly skilled personnel. It would be especially desirable to have the means for switching runners to be versatile and interchangeable amongst various mold components. Such a means of switching runners would lead to increased productivity and utilization of multi-impression molds at a low cost. The injection molding industry would welcome such an approach, especially if the method or apparatus could be easily modified or interchanged by the end user.